Structure diversity and anion exchange property of zinc(II) coordination polymers with flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene

Abstract

Flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene (L) was used to react with various zinc(II) salts ZnX [X = (BF 4) 2, SO 4, Cl 2, Br 2, I 2] to afford a series of coordination polymers with different structures. {[Zn(L) 2](BF 4) 2} n ( 1) has an infinite 2D cationic double layered structure, while {[Zn 4(L) 3(SO 4) 4] · 9H 2O} n ( 2) possesses a 3D framework structure with two different kinds of channels. The structure of [Zn 3(L) 2Cl 6] n ( 3) is 2D network and the one of {[Zn 3(L) 2Br 6] · CH 3OH} n ( 4) is an infinite 1D zigzag chain in a plywood-like stacking fashion. {[Zn(L)I]I} n ( 5) has 2D network structure which is further linked by hydrogen bonds to give rise to a fascinating 3D interlocked framework with twofold interpenetration. The results demonstrated that the counteranions have drastic effects on the structure of the coordination polymers. On the other hand, the flexible ligand L acts as a three-connecting node to connect three zinc(II) centers with different conformations. In 1 and 5, L has cis, cis, cis-conformation, while in 2, it adopts cis, trans, trans-conformation. It is interesting that two different conformations ( cis, cis, cis and cis, trans, trans) of L coexist in 3 and in the case of 4, the ligand L adopts a special trans-conformation. The results attest that the flexible ligand L can adopt different conformations to form complexes with varied structures. In addition, the uncoordinated tetrafluoroborate anions in 1 can be exchanged by nitrate or nitrite anions, which mean that 1 has anion exchange property.